Adsorption-desorption of hydrophilic contaminants rhodamine B with/without Cd 2+ on a coastal soil: implications for mariculture and seafood safety

Abstract

An experimental study on adsorption and desorption behaviors of rhodamine B (RhB) with/without cadmium ion (Cd²⁺) on a coastal soil was carried out in the face of the scarce studies on its environmental behaviors, especially its combined pollution with metal ions. The implications on mariculture and seafood safety, rarely concerned either, were also analyzed for providing a new insight between azo dyes and them. It showed that the adsorption of RhB on the tested soil was affected by Cd²⁺ and could be better fitted by the Freundlich model and dominantly identified as chemical adsorption according to the threshold of ΔG⁰ (40 kJ/mol). There is a positive hysteresis on the desorption of RhB, which was generally strengthened with the increasing concentration of RhB but generally weakened in the presence of Cd²⁺. The azo dyes including RhB and heavy metals such as Cd, as the major class of typical pollutants in coastal environment, are closely related to the mariculture and seafood safety. In the consideration of three aspects including potential pollutants for the mariculture, potential risks for seafood safety, and potential relationships between dyes and mariculture and seafood safety, their implications were further clarified.

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